Field of the Invention
The present invention relates to water quality sensors for household appliances. Particularly, the present invention relates to the water quality sensor utilizing backscattered light to determine the turbidity level of cleaning water in the household appliances to enhance the accuracy of turbidity detection, and also having a simple structure to reduce the fouling on the sensor.
Description of the Prior Art
With the development of technology, there are more and more household appliances for people to do housework in a time-saving fashion. Among these house appliances, washing appliances, such as the laundry machine and the dishwasher, are those utilizing liquid water containing detergent as the cleaning medium to clean articles, such that the efforts and time can be reduced compared to hand-washing.
Typically, washing appliances, e.g. the laundry machine and the dishwasher, are provided with the water quality sensor in the inner space for washing of the appliance, by which the turbidity or conductivity of the water can be determined. As disclosed in U.S. Pat. No. 5,596,408 and U.S. Pat. No. 6,771,373, a turbidity sensor has a housing having two finger protrusions which cleaning water is flowing in-between. The light emitting element and the light receiving element are face-to-face and separately positioned inside each finger protrusion of the housing. As the light emitting element generates a detecting beam passing through the transparent side of the housing, the particles in the water scatters away some portion of the detecting beam and allow the remaining portion to be transmitted through the water and be received by the light receiving element of the other side. So that by calculating the portion of detecting beam through the water and received by the light receiving element, the turbidity of the water can be determined. When the turbidity of water is detected at a predetermined level, the machine can be automatedly refilled with clean water to enhance the washing quality. However, turbidity detection becomes very inaccurate at low turbidity level. And, the fouling on the finger-type protrusion could also reduce the accuracy of detection and shorten the life-time of the sensor.
Also, a water quality sensor can further comprise a conductivity sensor. The conductivity sensor has two electrodes, which are controlled by a built-in microcontroller unit (MCU) of the washing appliance, to discharge in the cleaning medium. Generally, the velocity of electrons moving in water would be substantially constant, and may vary if there are ions (e.g. ions generated by the detergent dissolved in water) existing in the liquid water. In such case, an analog signal such as a voltage signal or a current signal would be obtained from the two electrodes by the MCU, and would be transmitted to an analog-to-digital converter (ADC). The analog signal would be converted by the ADC to a digital signal, such as a value of conductivity or a pH value. Compared to the constant conductivity or pH value of water in a general situation, the MCU could determine if there is any foreign ion existing in the liquid water based on the digital signal, so as to further determine if the washing needs to continue.
Nevertheless, with the increasing functionality of various washing appliances, it requires more and more sensors, such as a temperature sensor besides the turbidity sensor and the conductivity sensor mentioned above, to be configured and function within the washing appliance, and thereby the computing burden of the built-in MCU of the appliance would be significantly increased. In order to determine if one specific function of the washing appliance is to operate, the built-in MCU has to provide the control signals to the respective sensors, receive the analog signals returned from the respective sensors, transmit the respective analog signals to the ADC to convert these signals to a respective digital signal, and determine the functions of the washing appliance to be operate based on these digital signals. Such increased computing burden causes the possibility of error or abnormality for the built-in MCU.
The error or abnormality caused by the heavy computing burden of the built-in MCU may result in a malfunction thereof, and thereby the water quality sensor may keep discharging in the cleaning medium inside the washing appliance. In such case, the user will possibly get an electric shock from the washing appliance or the cleaning medium while touching the same.
A need thus exists for improved water quality sensors for improving the accuracy of detection, and for avoiding the error and abnormality of the built-in MCU of the household appliance that is caused by the increased computing burden of the MCU.